1. Field of the invention
This invention relates to a method for the formation of images and an apparatus for performing the same using a photosensitive and pressure-sensitive sheet, said method and said apparatus comprising an improved sheet-transportation system.
2. Description of the prior art
A method for the formation of images using a photosensitive sheet coated with pressure-rupturable capsules made of resin containing a chromogenic material and a photosensitive material that is hardened by light has been proposed by, for example, Japanese Laid-Open Patent Publication No. 58-88739. In this method, when the photosensitive sheet is exposed to light reflected from an original image or a laser beam or the like (light-exposure process), such light selectively illuminates the photosensitive sheet so that some of the pressure-rupturable capsules thereon receive the light to be hardened while others do not receive the light and remain unchanged, resulting in a latent image on the photosensitive sheet. Thereafter, an image-receiving sheet coated with developing materials for coloring the above-mentioned chromogenic materials is pressed against the latent image of the photosensitive sheet (pressure-transfer process), allowing the unhardened pressure-rupturable capsules to rupture. This causes the chromogenic materials contained in the pressure-rupturable capsules to flow out and react with the developing materials, thus obtaining a colored image on the image-receiving sheet.
Generally, the photosensitive sheet is used in a rolled form for continuous supply into an exposure and a pressure-transfer section. The light-exposure process is carried out in the exposure section either by scanning exposure or by entire surface exposure, the entire surface exposure method whereby an entire image-forming area is exposed at once having the advantage of a shorter exposure time than the time required for the scanning exposure.
However, the entire surface exposure method requires that the photosensitive sheet remain stationary during the light-exposure process before being transported into the pressure-transfer section for the pressure-transfer process. Furthermore, because the pressure-transfer process requires a high pressure (approximately 90kg/cm.sup.2), a pressure roller capable of applying a high pressure is used, and the photosensitive sheet should be transported at a low speed. Thus, when a plurality of sheets are to be printed with use of a conventional apparatus utilizing the entire surface exposure method, it is impossible to simultaneously perform the light-exposure process for an image-forming area and the pressure-transfer process for another image-forming area. Also in such an apparatus, because of the low speed pressure-transfer operation, there is no possibility of shortening the total time required for image forming processing. Furthermore, in the conventional method, when a plurality of sheets are to be printed, the pressure-transfer process for the first image-forming area of the photosensitive sheet is performed after completion of the light-exposure process for the same area, and then the same procedure is repeated for the second and subsequent image-forming areas. In such a conventional image-forming process, a relatively large portion of the photosensitive sheet between the light-exposure and pressure-transfer sections is left unused, and this unused portion is interposed between every pair of adjacent image-forming areas, thus wasting the photosensitive sheet.
Also, since the unhardened pressurerupturable capsules, as noted previously, are made to rupture by pressure, if the surface (capsule-coated side) of the photosensitive sheet remains in contact with transport rollers, etc. for a long time during the image-forming operation, the unhardened pressurerupturable capsules thereon may be flawed, resulting in black streaks and other image quality defects in a final colored image.